1. Field of the Invention
The field of the invention relates to a system for reducing the diameter of a honeycomb seal.
2. Background of the Invention
Honeycomb seals have been used for a number of years in gas turbine engines and other applications where a strong but light weight seal is required. The seals are manufactured by shaping strips of sheet stock to appropriate configurations, spot welding the strips to each other to form a cellular structure, and brazing the cellular structure to a backing plate in a vacuum furnace or the like. The strips are made from stainless steel, HASTALLOY-X, or any other material capable of being rolled into sheet stock. Cell diameters may be as small as about one fiftieth of an inch. U.S. Pat. No. 4,449,714 and U.K. Patent Application GB No. 2001692A both disclose honeycomb seals mounted to backing plates. Such seals may also be mounted to the interior walls of cylindrical substrates.
The height of the honeycomb seals usually must be reduced once it is brazed to the substrates. This has generally been accomplished by mechanical grinding processes, most or all of which require deburring of the honeycomb material after completion. In view of the fact that the foil used to manufacture honeycomb may be only 0.001-0.003" thick, it is quite delicate and easily damaged by this procedure.
Electrical discharge machining has been another approach for reducing the height of honeycomb seals. An electrode is used for discharging into the part while a dielectric oil controls the arc. There are several problems with the method as the oil is a contaminant for the honeycomb seal and cannot easily be flushed out. Waste oil with ground metal therein also poses a waste disposal problem.
An efficient method of reducing honeycomb seal height has been referred to as the spark erosion process. An electrode is positioned adjacent to a cylindrical workpiece having an interior honeycomb seal. The workpiece is rotated while the electrode moves axially with respect thereto. A series of electrical sparks, or arcs are generated between the electrode and the workpiece, thereby melting the surface of the seal. Water mixed with an anti-rusting solution is applied continuously to cool the seal and prevent molten metal from sticking to it.